1. Field
The present embodiments relate to an image processing equipment and a digital camera to apply a noise filtering using a multi-resolution analysis for an obtained image.
2. Description of the Related Art
A noise filtering using a multi-resolution analysis (hereinafter, called as a multi-resolution noise filtering) is known as one of methods to filter low-frequency noises appeared in an image data obtained by a digital camera and so on.
The multi-resolution noise filtering is an art in which noise filtering effects for reduced images generated with plural reduction ratios are reflected on an original sized image, and thereby, for example, the filtering of low-frequency noises spreading for several dozen pixels in a row direction and/or a column direction is achieved (refer to Japanese Unexamined Patent Application Publication No. 2000-224421).
For example, a down-sampling is applied to an original image with reduction ratios of one-fourth respectively in the row direction and the column direction to generate a reduced image in one-sixteenth, and low-frequency noise components in the original image can be estimated by performing an up-sampling using a linear interpolation on the noise components extracted from this reduced image. The low-frequency noise components estimated as stated above are subtracted from the original image, and thereby, the low-frequency noise components can be filtered from the original image.
In a recent high pixel digital camera, there is a case when the low-frequency noises spreading for several dozen pixels wide appear. It is necessary to prepare line memories storing an image data in a range larger than a range assumed to be a spread of the low-frequency noises so that the filtering of the low-frequency noises as stated above is promptly performed by a pipeline processing.
However, if such vast line memories are prepared, a significant increase in a circuit scale is caused, and it leads an increase in cost of an image processing circuit.